Heat-sensitive color-forming recording material and process for preparation thereof

ABSTRACT

Disclosed is a heat-sensitive color-forming recording material which comprises a recording layer comprising a particulate phenolic color developer and a particulate leuco pigment, which are dispersed in a binder independently from each other, wherein the phenolic color developer and/or leuco pigment is present in the form of compatible solid particles with a substantially inactive organic solid medium having a melting or softening point lower than that of the phenolic color developer and/or leuco pigment and said organic solid medium is present in said compatible solid particles in an amount .[.2 to 250 times as large as.]. .Iadd.of 0.2 to 250% by weight, based on .Iaddend.the amount of the phenolic color developer and/or leuco pigment on the weight base. This heat-sensitized color-forming recording material is highly sensitive without substantial increase of the fog density.

This application is a division, of application Ser. No. 346,772, filedFeb. 8, 1982, now abandoned.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a heat-sensitive color-formingrecording material. More particularly, the present invention relates toa heat-sensitive recording material which is sensitized withoutsubstantial increase of the fog density.

(2) Description of the Prior Art

The combination of a leuco pigment and a color developer composed of anacidic substance has been widely used for recording of informations, forexample, heat-sensitive recording, pressure-sensitive recording andelectrostatic photographic recording. For example, as a recordingelement for heat-sensitive recording, there has been used a recordingmaterial comprising a recording layer formed on a substrate, saidrecording layer being obtained by dispersing a leuco pigment which iscolorless or has a light color in the normal state and a phenol which issolid at normal temperature but is heat-fusible, in a polymeric binderindependently in separate phases.

In this heat-sensitive recording material, color formation is effectedwhen the leuco pigment and phenolic color developer are reacted witheach other in the state activated by heat, especially in the fusedstate. Since fusion of the phenolic color developer or leuco pigment isnot caused unless the temperature is considerably high, the heatsensitivity of the recording material is low and the density of arecorded image is generally low. Furthermore, since recording must becarried out at a high temperature, this recording material isdisadvantageous in that a high temperature heat source is necessary.Moreover, the temperature of a transportation system in a heat-sensitiverecording apparatus is elevated, and therefore, fogging is readilycaused to occur.

SUMMARY OF THE INVENTION

I found that when such phenolic color developer and/or leuco pigment isdispersed in a binder in the form of compatible solid particles with asubstantially inactive organic solid medium which has a melting point orsoftening point lower than the melting point of the phenolic colordeveloper and/or leuco pigment and also has a compatibility with thephenolic color developer and/or leuco pigment and a recording layer isformed from this dispersion, the heat sensitivity can be prominentlyimproved without substantial increase of the fog density.

More specifically, in accordance with the present invention, there isprovided a heat-sensitive color-forming recording material whichcomprises a recording layer comprising a particulate phenolic colordeveloper and a particulate leuco pigment, which are dispersed in abinder independently from each other, wherein the phenolic colordeveloper and/or leuco pigment is present in the form of compatiblesolid particles with a substantially inactive organic solid mediumhaving a melting or softening point lower than that of the phenoliccolor developer and/or leuco pigment and said organic solid medium ispresent in said compatible solid particles in an amount 2 to 250 timesas large as the amount of the phenolic color developer and/or leucopigment on the weight base.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relation between the heating temperatureand the reflection density in heat-sensitive recording materialsaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The phenolic color developer that is used in the present invention issolid at normal temperature and is heat-fusible and it is a prototropicphenol in the fuse state. As preferred examples of the phenolic colordeveloper, there can be mentioned 4,4'-isopropylidene diphenol(bisphenol A), 4,4'-methylene-bis(phenol),4,4'-isopropylidene-bis(2-chlorophenol),4,4'-isopropylidene-bis(2,6-dichlorophenol),4,4'-isopropylidene-bis(2-methylphenol),4,4'-isopropylidene-bis(2-tert-butylphenol),4,4'-sec-isobutylidene-bis(2-methylphenol),4,4'-cyclohexylidene-diphenol, 2,2'-thiobis(4,6-dichlorophenol),p-tert-butylphenol, 3,4-dichlorodiphenol, o,o'-diphenol,4-hydroxydiphenoxide, 2,2'-dihydroxy-bisphenol,2,2'-methylene-bis(4-chlorophenol), 2,6-dihydroxybenzoic acid and1-hydroxy-2-napthoic acid.

All the leuco pigments customarily used for heat-sensitive recordingmaterials of this type can be used in the present invention. Forexample, triphenylmethane leuco pigments, fluoran type leuco pigments,spirooyran type leuco pigments, rhodamine lactam type pigments, auraminetype leuco pigments and phenothiazine type leuco pigments may be usedsingly or in combination. Preferred examples are as follows.

Triphenylmethane type leuco pigments

3,3-Bis(p-dimethylaminophenyl)phthalide,3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide,3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide,3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide,3,3-bis(p-dimethylaminophenyl)-6-methoxyphthalide,4-hydroxy-4'-dimethyl-aminotriphenylmethane-lactone, and4,4'-bishydroxy-3,3'-bis-diaminotriphenylmethane-lactone.

Fluoran type leuco pigments

3-Dimethylamino-5,7-dimethylfluoran, 3-diethylamino-5,7-dimethylfluoran,3-diethylamino-6,7-dimethylfluoran, 3-cyclohexylamino-6-chlorofluoran,3-dimethylamino-6-methoxyfluoran, 3,6-bis-β-methoxyethoxyfluoran,3-diethylamino-7-dibenzylaminofluoran,3-diethylamino-6-methyl-7-chlorofluoran,3-diethylamino-6-methyl-7-anilinofluoran, 3,7-bisdiethylaminofluoran and3-diethylamino-7-methoxyfluoran.

Spiropyran type leuco pigments

8'-Methoxybenzoindolinospiropyran,3-phenyl-8'-methoxybenzoindolinospiropyran,6'-chloro-8'-methoxybenzoindolinospiropyran,5,6'-dichloro-8'-methoxybenzoindolinospiropyran,4,7,8'-trimethoxybenzoindolinospiropyran, benzo-β-naphthospiropyran,3-methyl-di-β-naphthospiropyran and1,3,3-trimethyl-6'-chloro-8'-methoxyindolinobenzospiropyran.

Rhodamine lactam type leuco pigments

9-(p-Nitroanilino)3,6-bis(diethylamino)-9-xanthyl-o-benzoic acid lactamand

2-[3,6-bis(diethylamino)-9-(o-chloroanilino)xanthyl]-benzoic acidlactam.

Auramine type leuco pigments

2,5-Dichloro-N-phenyl-leucoauramine,4,4'-bisdimethylamino-3,4-chlorophenyl-leucoauramine and4,4'-bis-dimethylaminopiperazine hydrol.

Phenothiazine leuco type pigments

Benzoyl leuco methylene blue, p-chlorobenzoyl leuco methylene blue,3,4-dichlorobenzoyl leuco methylene blue and p-methoxybenzoyl leucomethylene blue.

According to the present invention, the above-mentioned phenolic colordeveloper and/or leuco pigment is combined with a specific organic solidmedium which has a melting or softening point lower than that of thephenolic color developer and/or leuco pigment and is substantiallyinactive and compatible with the phenolic color developer and/or leucopigments, especially water-insoluble one, and the phenolic colordeveloper and/or leuco pigment is used in the form of compatible solidparticles with said organic solid medium.

As the solid medium, there are preferably used higher saturated fattyacids and their metal salts, amides, hydrazides, methylolated productsand esters, though applicable solid media are not limited to thesecompounds. As preferred examples of the higher saturated fatty acid,there can be mentioned those having 6 to 30 carbon atoms, such asstearic acid, palmitic acid, myristic acid, lauric acid and behenicacid. As the metal salt, there can be mentioned zinc salts, calciumsalts, magnesium salts, lead salts, cadmium salts, barium salts andaluminum salts. As the amide, there can be used not only monoamides ofthe above-mentioned fatty acids but also bis-amides such asethylene-bis-stearylamide. As the hydrazide, there can be usedhydrazides of the above-mentioned fatty acids. As the methylolatedproduct, there can be used methylolated products of the above-mentionedfatty acid amides, such as stearylmethylolamide. As the ester, there canbe used triglyceride and glycol diesters of the above-mentioned fattyacids, such as beef tallow and hardened oil, sorbitan monoesters of theabove-mentioned fatty acids, esters of the above-mentioned fatty acidswith higher alcohols such as cetyl alcohol, and esters of theabove-mentioned fatty acids with polyhydric alcohols such as ethyleneglycol and propylene glycol.

As other preferred examples of organic solid medium, there can bementioned higher alcohols having 16 to 30 carbon atoms, such as cetylalcohol and stearyl alcohol, oxidized polyethylene waxes and alcohol-and acid-modified oxidized polyethylene waxes, microcrystalline wax, andnatural waxes such as carnauba wax, candelilla wax and bees wax.

Furthermore, there may be used low-molecular-weight polymers of vinylaromatic compounds such as styrene and vinyltoluene andlow-molecular-weight polymers of nitrogen-containing heterocyclic vinylcompounds such as 2-vinylpyridine.

The kinds of organic solid media that can be used in the presentinvention are not limited to those exemplified above. For example,antioxidants, thermal stabilizers and ultraviolet ray absorbers may beused, so far as they are substantially inactive and compatible with thephenolic color developer or leuco pigments and have a melting pointlower than that of the phenolic color developer or leuco pigment.Examples of the solid medium of this type include sterically hinderedphenols such as 2,6-di-tert-butyl-p-cresol,2,2-methylene-bis(4-ethyl-6-tert-butylphenol),2-hydroxy-4-methoxybenzophenone, phenyl salicylate, p-tertbutylsalicylate and 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, andsulfur-containing organic compounds such as pentaerythritoltetrakis(β-laurylthiopropionate), zinc dibutyldithiocarbamate and4,4'-dithiomorpholine.

High density polyethylene waxes and similar non-polar waxes becomesincompatible with the phenolic color developer or leuco pigment whentheir molecular weights are increased. Accordingly, use of these waxesare not preferred for attaining the objects of the present invention.When the recording layer is formed by using an aqueous coatingcomposition, use of a water-soluble solid medium such as an alkali metalsalt of a higher fatty acid is not preferred because such solid mediumis readily dissolved into water.

Moreover, an acidic solid medium such as a high fatty acid is notpreferred as the solid medium for formation of compatible solidparticles with the leuco pigment, because color formation takes placewhen such solid particles are prepared.

When both the leuco pigment and the phenolic color developer are usedsimultaneously for formation of compatible solid particles, it ispreferred that a solid medium which is compatible with both the leucopigment and the phenolic color developer, such as a fatty acid amide, beused.

In the present invention, when the phenolic color developer and/or leucopigment is dispersed and made present in the binder of the recordinglayer in the form of compatible solid particles with the above-mentionedsolid medium, the heat sensitivity is prominently improved over thesensitivity attained when the phenolic color developer or leuco pigmentis singly incorporated into the binder in the form of particles. Forexample, when a color former composed of bisphenol A is employed andparticles of this color developer are dispersed in a binder, there isobtained only an image having a reflection density of 0.35 at 120° C.,whereas when bisphenol A is used in the form of compatible solidparticles with ethylene-bis-stearylamide, the reflection image densityis increased to 1.05, that is, a level 3 times as high as the abovereflection density, under the same recording conditions. It is believedthat the reason is that the melting point of the phenolic colordeveloper is reduced in the form of the above-mentioned compatible solidparticles, the prototropy becomes possible at a lower temperature.Furthermore, for example, when a leuco pigment composed of CrystalViolet Lactone is used, if recording is carried out at 110° C., an imagehaving a reflection density of only 0.40 is obtained. On the other hand,when Crystal Violet Lacton is used in the form of compatible solidparticles with 10% by weight of an oxidized polyethylene wax, an imagehaving a reflection density of 0.76 can be obtained and the reflectiondensity is increased to a level about 2 times as high as the abovereflection density. It is believed that the reason is that the meltingpoint of the leuco pigment is reduced in the form of the above-mentionedcompatible solid particles and activation of the leuco pigment becomespossible at a lower temperature.

In the present invention, it is important that the above-mentioned solidmedium should be used in an amount .[.2 to 250 times, especially 5 to100 times,.]. .Iadd.of 0.2 to 250%, preferably 5 to 100% by weight,based on .Iaddend.the amount of the phenolic color developer and/orleuco pigment on the weight base. When the amount of the solid medium istoo small and below the above range, the degree of reduction of themelting point is low and no prominent improvement of the heatsensitivity can be attained. On the other hand, if the amount of thesolid medium is too large and is beyond the above range, the entireconcentration of the phenolic color developer or leuco pigment isreduced, and consequently, the image density is lowered.

In the present invention, the above-mentioned compatible solid particlesare prepared according to any of the following methods.

According to the first method of the present invention, a phenolic colordeveloper or leuco pigment and a substantially inactive organic solidmedium which has a melting or softening point lower than that of thephenolic color developer or leuco pigment and is compatible with thephenolic color developer or leuco pigments are dissolved in a solventfor them to form a mixed solution, and this solution is then mixed witha precipitating medium which is miscible with said solvent but is anon-solvent for the color developer or pigment and the solid medium toprecipitate compatible solid particles of the phenolic color developeror leuco pigment and the organic solid medium.

As the solvent, a water-miscible organic solvent is preferably used, andas the non-solvent, water is preferably used. As the water-miscibleorganic solvent, there can be mentioned, for example, alcohols such asmethanol, ethanol, propanol and diacetone alcohol, ketones such asacetone and methylethyl ketone, cyclic ethers such as dioxane andtetrahydrofuran, esters such as methyl cellosolve acetate, carbitolacetate and methylcarbitol acetate, sulfoxides such asdimethylsulfoxide, N,N-di-substituted amides such as dimethylformamideand dimethylacetamide, and lactones such as γ-valerolactone. Thephenolic color developer or leuco pigment and the organic solid mediumare dissolved in the organic solvent at the above-mentioned ratio sothat the entire solid concentration is 10 to 50% by weight, especially20 to 40% by weight. The resulting solution is mixed with water at aweight ratio of from 1/5 to 1/30, especially from 1/10 to 1/20, wherebycompatible solid particles are precipitated, and these particles arethen filtered, washed with water and dried according to need.

According to the second method of the present invention, a phenoliccolor developer or leuco pigment and a substantially inactive organicsolid medium which has a melting or softening point lower than that ofthe phenolic color developer or leuco pigment and is compatibletherewith are dissolved in a solvent for them at a high temperature anda high concentration to form a mixed solution, and the resultingsolution is cooled to precipitate compatible solid particles of thephenolic color developer or leuco pigment and the organic solid medium.

As the organic solvent, there may be used not only the above-mentionedwater-miscible organic solvents but also aromatic solvents such asbenzene, toluene and xylene and halogenated hydrocarbon solvents such aschlorobenzene, and solvents having a high boiling point are especiallypreferred. It is preferred that the difference between the hightemperature adopted for dissolution and the low temperature adopted forprecipitation be at least 50° C., especially at least 70° C.

According to the third method, a mixture of a phenolic color developeror leuco pigment and a substantially inactive organic solid medium whichhas a melting or softening point lower than that of the phenolic colordeveloper or leuco pigment and is compatible therewith is molten, andthe melt is granulated after cooling or under cooling to form compatiblesolid particles of the phenolic color developer or leuco pigment and theorganic solid medium. For granulation of the melt, there may be adopteda method in which a cooled melt is pulverized and is then sieved ifnecessary, and a method in which the melt is subjected to spraygranulation.

From the viewpoints of the resolving power and the heat sensitivity, itis preferred that the number average particle size of the compatiblesolid particles be 0.1 to 3 microns, especially 0.2 to 2 microns.

Water-soluble and water-dispersible binders customarily used forheat-sensitive recording materials of this type can be used as thebinder in the present invention. As preferred examples, there can bementioned polyvinyl alcohol, starch, carboxymethylated starch,hydroxyethylated starch, carboxymethyl cellulose, ethyl cellulose, gumarabic, gelatin, casein, polyvinyl pyrrolidone, polyacrylamide,styrene-maleic acid salt copolymers, vinyl ether-maleic acid saltcopolymers and styrenebutadiene copolymer latices.

The phenolic color developer and leuco pigment, at least one of which isin the form of the above-mentioned compatible solid particles, aredispersed in an aqueous medium containing the above-mentionedwater-soluble or water-dispersible binder to form a coating liquid.

In the present invention, it is preferred that the leuco pigment (A) andthe phenolic color developer (B) be used at a weight ratio (A)/(B) offrom 1/2.0 to 1/40, especially from 1/2.5 to 1/20. It also is preferredthat the leuco pigment be made present in the recording layer in anamount of 2 to 30% by weight, especially 5 to 20% by weight, as drysolids based on the total composition. If the amount of the leucopigment or phenolic color developer is too small and below the aboverange, the color density is reduced, and if the amount of the leucopigment or phenolic color developer is increased beyond the above range,no particular improvement of the color density or other quality can beattained, but an economical disadvantage is brought about.

It is preferred that the binder be used in an amount of 20 to 80% byweight, especially 25 to 60% by weight, based on the sum of the amountsof the leuco pigment and phenolic color developer, at least one of whichis in the form of the above-mentioned compatible solid particles.

For preparation of this coating liquid, there is preferably adopted amethod in which one of the leuco pigment and phenolic color developer,at least one of which is in the form of the compatible solid particles,is added to a solution of the water-soluble or water-dispersible binder,the mixture is wet-pulverized to form a dispersion, and the othercomponent is directly added to the dispersion or a dispersion of theother component is prepared in the same manner as described above andboth the dispersions are mixed. From the viewpoint of the adaptabilityto the coating operation, it is preferred that the solid concentrationof the coating liquid be 8 to 20% by weight.

In order to improve various characteristics of the heat-sensitiverecording layer, known additives may be added to the coating liquidaccording to known recipes. For instance, in order to improve thewhiteness of the recording layer or attain a bulking effect, a whitepigment such as titanium dioxide or a filler such as a clay or calciumcarbonate may be added. Furthermore, in order to adjust the recordingsensitivity, there may be added an animal, vegetable or mineral wax suchas paraffin wax or carnauba wax, stearic acid, an amide, soap or otherderivative of a higher fatty acid or a synthetic waxy substance such asa polyethylene wax, a polypropylene wax or a polyethylene glycol.Moreover, in order to prevent coloration of the background, there may beadded an alkanolamine such as triethanolamine or other organic base.Still further, there may be added a water resistance-imparting agent anda defoaming agent.

As the substrate on which the recording layer is to be formed, there canoptionally be used papers, non-woven fabrics, artificial papers, variousfilms, metal foils and laminates thereof. It is preferred that the basisamount of the recording layer be 2 to 10 g/m², especially 3 to 8 g/m²,in the dry state.

The heat-sensitive recording element of the present invention canvaluably be used as a recording element of a thermal head, a thermalpen, an infrared flash lamp or a laser device, which is used as thelight source of a facsimile printer, a data communication device, acomputer console unit, a measurement device, a passometer, a copyingmachine or the like.

The present invention will now be described in detail with reference tothe following Examples that by no means limit the scope of theinvention.

EXAMPLE 1

A mixture of 5 g of bisphenol A [2,2-bis(4'-hydroxyphenyl)propane] and10, 25, 50, 100, 200, 300, 500, 1000, 2000, 3000 or 5000 mg of a fattyacid amide (a formaldehyde condensate of a mixture containing stearicacid amide and palmitic acid amide at a weight ratio of about 7/3) wasdissolved in 10 to 15 g of diacetone alcohol under heating (120° C.),and the solution was gradually added to 300 ml of water and the mixturewas stirred strongly. The formed white precipitate was washed withwater, filtered and dried in an oven maintained at 60° C.

The melting point of the so-prepared solid solution of bisphenol A andfatty acid amide was measured by a commercially available melting pointmeasuring device (Micro Melting Point Apparatus Model No. 428 suppliedby Shibayama Seisakusho). The obtained results are shown in Table 1.

From the results shown in Table 1, it will readily be understood thatthe melting-initiating temperature of bisphenol A is lowered if it isformed into a solid solution with the fatty acid amide.

                  TABLE 1                                                         ______________________________________                                                                  Melting Temperature                                                           Range (°C.) (melting-                                   Content*       initiating temperature                                         (% by weight)  to melting-completing                               Compound   of Fatty Acid Amide                                                                          temperature)                                        ______________________________________                                        bisphenol A                                                                              --             156 (single substance)                              fatty acid amide                                                                         --             143 (single substance)                              solid solution (1)                                                                       0.2            132-156                                             solid solution (2)                                                                       0.5            120-154                                             solid solution (3)                                                                       1.0            115-154                                             solid solution (4)                                                                       2.0            105-156                                             solid solution (5)                                                                       4.0            94-156                                              solid solution (6)                                                                       6.0            105-152                                             solid solution (7)                                                                       10             95-155                                              solid solution (8)                                                                       20             81-151                                              solid solution (9)                                                                       40             78-140                                              solid solution (10)                                                                      60             68-116                                              solid solution (11)                                                                      100            78-112                                              ______________________________________                                         Note:                                                                         *the amount (% by weight based on bisphenol A) of the fatty acid amide        solid disolved in bisphenol A                                            

EXAMPLE 2

In the same manner as described in Example 1, 5 g of bisphenol A and 0.2g (2% by weight) of a compound shown in Table 2 were commonly dissolvedand precipitated to form solid solutions. The melting temperature rangesof the solid solutions were measured to obtain the results shown inTable 2.

                  TABLE 2                                                         ______________________________________                                                                    Melting Tempera-                                  Compound        Composition ture Range (°C.)                           ______________________________________                                        Compound of Example 1                                                                         solid solu-.sup.1*                                                                        106-154                                                           tion(a)                                                       Compound of Example 1                                                                         solid solu-*.sup.2                                                                        111-156                                                           tion(b)                                                       Compound of Example 1                                                                         solid solu-*.sup.3                                                                        105-156                                                           tion(c)                                                       ethylene-bis stearic                                                                          single      141-145                                           acid amide      substance                                                     ethylene-bis stearic                                                                          solid solu- 112-156                                           acid amide      tion(d)                                                       7/3 mixture of stearic acid                                                                   single sub-  98-101                                           amide and palmitic acid amide                                                                 stance                                                        7/3 mixture of stearic acid                                                                   solid solu-  95-151                                           amide and palmitic acid amide                                                                 tion(e)                                                       zinc stearate   single      122                                                               substance                                                     zinc stearate   solid solu- 121-154                                                           tion(f)                                                       mixture of stearic acid amide                                                                 single      104                                               and vehenic acid amide                                                                        substance                                                     mixture of stearic acid amide                                                                 solid solu- 112-161                                           and vehenic acid amide                                                                        tion(g)                                                       4,4'-dithiodimorpholine                                                                       single      122                                                               substance                                                     4,1'-dithiodimorpholine                                                                       solid solu-  81-156                                                           tion(h)                                                       zinc dibutyldithiocarbamate                                                                   single      104                                                               substance                                                     zinc dibutyldithiocarbamate                                                                   solid solu- 102-151                                                           tion(i)                                                       oxidized low density                                                                          single      110                                               polyethylene wax                                                                              substance                                                     oxidized low density                                                                          solid solu- 103-156                                           polyethylene wax                                                                              ion(j)                                                        ______________________________________                                         Note:                                                                         *.sup.1 solid solution(4) of Example 1 having an amide content of 2%          *.sup.2 tetrahydrofuran was used instead of diacetone alcohol, dissolutio     was effected at room temperature and precipitation was then conducted         *.sup.3 after heating dissolution, water was poured into the solution to      effect precipitation                                                     

From the results shown in Table 2, it will readily be understood thatthe melting-initiating temperature is lowered by formation of the solidsolution.

EXAMPLE 3

In a ball mill, 100 parts by weight (all "parts" given hereinafter areby weight) of the solid solution obtained in Example 1, 670 parts of anaqueous solution containing 5% by weight of polyvinyl alcohol and 100parts of water were mixed and pulverized for 5 hours to form a liquid A(A-1 through A-11).

In a ball mill, 50 parts of Crystal Violet Lactone, 330 parts of anaqueous solution containing 5% by weight of polyvinyl alcohol and 50parts of water were mixed and pulverized for 5 hours to form a liquid B.

For comparison, in the same manner as described above with respect tothe liquid A, a liquid A' was prepared by using 100 parts of bisphenol A(comparative color former).

The so formed liquid A or A' was mixed with the liquid B so that theweight ratio of the phenolic color developer to Crystal Violet Lactonewas 5, and the resulting coating liquid was coated on a slick paperhaving a basis weight of 55 g/m² by a wire bar and dried at 60° C. toform a heat-sensitive recording paper having a coating amount of about 5g/m² on the dry basis. The heat-sensitive recording paper was passed ata speed of 4 cm/sec between rotary heater rollers (pressed under 1Kg/cm; surface temperature=130° C.) to effect coloration under heating.The reflection density was measured by a commercially availabledensitometer (Macbeth RD-514) provided with a red filter. The obtainedresults are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Color Former      Reflection Density                                          ______________________________________                                        comparative color developer                                                                     0.80                                                        (bisphenol A)                                                                 color developer of present                                                    invention                                                                     solid solution (1)                                                                              1.05                                                        solid solution (2)                                                                              1.12                                                        solid solution (3)                                                                              1.13                                                        solid solution (4)                                                                              1.15                                                        solid solution (5)                                                                              1.18                                                        solid solution (6)                                                                              1.20                                                        solid solution (7)                                                                              1.23                                                        solid solution (8)                                                                              1.25                                                        solid solution (9)                                                                              1.23                                                        solid solution (10                                                                              1.18                                                        solid solution (11)                                                                             0.98                                                        ______________________________________                                    

From the results shown in Table 3, it will readily be understood that ahighest sensitizing effect is obtained in the solid solutions (7) and(8), namely when the amount of the acid amide to be solid-dissolved is10 to 40%, while the sensitizing effect is reduced if the amount of theacid amide solid-dissolved is increased beyond this level. It wasconfirmed that if the amount of the acid amide solid-dissolved is 30% orlarger, there is not a pressure-sensitive color-forming characteristic.That is, no color was formed even if the recording layer was scratchedby a wire, a spike or a nail.

EXAMPLE 4

In the same manner as described in Example 3, a coating liquid wasprepared by using the color developer (solid solution) of Example 2. Thecoating liquid was coated on a slick paper having a basis weight of 55g/m² by a wire bar and dried at 60° C. to form a heat-sensitiverecording paper having a coating amount of about 5 g/m² on the dry base.The heat-sensitive recording paper was passed at a speed of 4 cm/secbetween heater rollers at various heating temperatures to effect colorformation. The reflection density was measured. The obtained results areshown in FIG. 1.

In FIG. 1, curve Blank shows the results obtained when bisphenol A alonewas used, and curves A through J show the results obtained when thesolid solutions (a) through (j) shown in Table 2 were used,respectively. In case of each of the curves A through J, the formedcolor had a higher density than that of the formed color in case of thecurve Blank, if the comparison was made at the same heating temperature.

When a fluoran type leuco pigment, a spiropyran type leuco pigment, aRhodamine type leuco pigment, an Auramine type leuco pigment or aphenothiadine type leuco pigment was used instead of thetriphenylmethane type leuco pigment such as Crystal Violet Lactone,similar results were obtained.

EXAMPLE 5

Color developer described below were prepared by using the fatty acidamide used in Example 1 and bisphenol A, and they were subjected to thecomparative test.

Comparative color developer 1

Bisphenol A alone was used as the color developer.

Comparative color developer 2

A mere mixture of 100 parts of the fatty acid amide used in Example 1and 50 parts of bisphenol A was used as the color developer.

Color developer 3 of present invention

A mixture of 100 parts of the fatty acid amide used in Example 1 and 50parts of bisphenol A was heated and molten at 160° C. to dissolve themin each other sufficiently, and the melt was cooled and pulverized toform a solid solution which was used as the color developer.

In the same manner as described in Example 3, 100 parts of the colordeveloper, 670 parts of an aqueous solution containing 5% by weight ofpolyvinyl alcohol and 100 parts of water were mixed and pulverized toform a color developer dispersion A-(1), A(2) and A-(3).

In the same manner as described above, a dispersion containing 50 partsof Crystal Violet Lactone (liquid B) was prepared.

A coating liquid was prepared by mixing 5 parts of the liquid B with25.3 parts of the dispersion A-(1) or 76 parts of the dispersion A-(2)and A-(3) so that the amount of bisphenol A of the color developercomponent was 5 times the amount of Crystal Violet Lactone. The coatingliquid was coated on a slick paper and dried at 60° C. to form aheat-sensitive recording paper (having a coating amount of about 6g/m²). The heat-sensitive and pressure-sensitive color-formingcharacteristics of the recording paper were examined. The obtainedresults are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                 Heat-Sensitive Color                                                          Formation (reflection                                                                       Pressure-Sensitive                                              density       Color Formation                                        Color Developer                                                                          120° C.                                                                        130° C.                                                                        140° C.                                                                      (scratched by nail)                          ______________________________________                                        1 (compar- 0.35    0.83    1.05  blue color formation                         ison                                                                          2 (compar- 0.20    0.31    0.67  no color formation                           sion                                                                          3 (presemt 0.42    0.92    1.10  no color formation                           invention                                                                     ______________________________________                                    

From the results shown in Table 4, it is seen that when the fatty acidamide is merely mixed with bisphenol A, the susceptibility to colorationunder pressure is effectively reduced but the heat sensitivity is ratherdegraded. It also is seen that in the heat-sensitive recording paperprepared according to the present invention, the heat sensitivity isexcellent and the effect of preventing color formation under pressure isvery good.

EXAMPLE 6

In order to examine the effects attained by using the color developer inthe form of a solid solution, the following comparative experiment wascarried out.

Preparation of Color Developer Dispersion (Liquid C)

C-1:

Bisphenol A alone

C-2:

A mixture (100/2) of bisphenol A and a fatty acid amide (formaldehydecondensate of a mixture containing stearic acid amide and palmitic acidamide at a weight ratio of about 7/3)

C-3:

A solid solution of C-2 (prepared in the same manner as described inExample 1)

C-4:

A mixture (100/2) of bisphenol A and ethylene-bis-stearic acid amide

C-5:

A solid solution of C-4 (prepared in the same manner as described inExample 1)

C-6:

A mixture (100/2) of bisphenol A and a fatty acid amide (a mixturecontaining stearic acid amide and palmitic acid amide at a weight ratioof about 7/3)

C-7:

A solid solution of C-6 (prepared in the same manner as described inExample 1)

C-8:

A mixture (100/2) of bisphenol A and zinc stearate

C-9:

A solid solution of C-8 (prepared in the same manner as described inExample 1)

In a ball mill, 100 parts of the color developer C, 170 parts of anaqueous solution containing 20% by weight of etherified starch and 340parts of water were mixed and pulverized for 5 hours to form a liquid C'(C'-1 through C'-9).

Preparation of Leuco Pigment Dispersion (Liquid D)

In a ball mill, 50 parts of Crystal Violet Lactone, 85 parts of anaqueous solution containing 20% by weight of etherified starch and 170parts of water were mixed and pulverized for 5 hours to obtain a liquidD.

Preparation of Coating Liquid (Liquid E)

Coating liquids E-1 through E-9 were prepared by mixing 5 parts of theliquid D with 25 parts of the liquid C'-1 or 25.5 parts of the liquidC'-2, C'-3, C'-4, C'-5, C'-6, C'-7, C'-8 or C'-9 so that the amount ofbisphenol A of the color developer component was 5 times the amount ofCrystal Violet Lactone.

The coating liquid was coated on a slick paper and dried to form aheat-sensitive recording paper having a coating amount of about 5 g/m²on the dry base. In the same manner as described in Example 4, colorformation was effected at various temperatures, and the reflectiondensity was measured. The obtained results are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                                  Reflection Density                                                            Heating Temperature (°C.)                                    Color Developer                                                                           100      110    120    130  140                                   ______________________________________                                        C-1 (blank) 0.25     0.32   10.48  0.80 1.17                                  C-2 (comparison)                                                                          0.25     0.34   0.55   0.84 1.06                                  C-3 (present inven-                                                                       0.30     0.64   1.10   1.34 1.42                                  tion)                                                                         C-4 (comparison)                                                                          0.24     0.32   0.51   0.94 1.21                                  C-5 (present inven-                                                                       0.28     0.57   0.92   129  1.39                                  tion)                                                                         C-6 (comparison)                                                                          0.44     0.58   0.76   1.01 1.09                                  C-7 (present inven-                                                                       0.67     1.01   1.11   1.26 1.30                                  tion)                                                                         C-8 (comparison)                                                                          0.25     0.32   0.46   0.88 1.05                                  C-9 (present inven-                                                                       0.25     0.32   0.55   0.92 1.15                                  tion)                                                                         ______________________________________                                    

From the results shown in Table 5, it will readily be understood thatwhen a phenolic color developer is made present in the form of a solidsolution with an organic solid medium having a compatibility with thephenolic color developer, the density of the formed color is increasedover the density obtained when the phenolic color developer is madepresent in the form of a mere mixture with the organic solid medium(both the components are independently dispersed).

As another method for formation of the solid solution, there could beadopted a method in which bisphenol A and the organic solid mediumcompatible therewith were dissolved in hot chlorobenzene (120° C.) at ahigh concentration (for example, 150%), the solution was cooled to 5° C.and filtered, and the collected precipitate was dried at 60° C. to forma solid solution. From the results of the experiment conductedseparately, it was confirmed that a color developer having a highsensitivity could be similarly obtained according to this method.

EXAMPLE 7

In the same manner as described in Example 3, a solid solution wasprepared except that bisphenol S [bis(4'-hydroxyphenyl)sulfone, meltingpoint=246.0° to 248° C.] was used instead of bisphenol A and a mixturecontaining stearic acid amide and palmitic acid amide at a ratio of 7/3was used as the fatty acid amide, and the color formation test wascarried out in the same manner as described in Example 3. The obtainedresults are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                  Reflection Density                                                            Composition (bisphenol S/fatty acid                                 Heating Temp-                                                                           amide) of Solid Solution                                            erature (°C.)                                                                    100/0    100/10  100/20 100/40                                                                              100/60                                ______________________________________                                        140       0.25     0.65    1.02   0.79  0.75                                  150       0.26     0.96    1.08   1.10  1.08                                  160       0.27     1.02    1.13   1.26  1.11                                  ______________________________________                                    

From the results shown in Table 6, it will readily be understood thatwhen the phenolic color developer is used in the form of a solidsolution with a compatible organic solid medium, the heat sensitivitycan be increased and a highest effect can be obtained when the contentof the organic solid medium in the solid solution is about 40% based onthe phenolic color developer.

EXAMPLE 8

In order to examine the effects attained by using a leuco pigment in theform of a solid solution, the following comparative experiment wascarried out.

Preparation of Leuco Pigment Dispersions (Liquid A')

A-1:

Crystal Violet Lactone alone

The following mixtures (comparisons) of Crystal Violet Lactone (A-1) anda fatty acid amide (a mixture containing stearic acid amide and palmiticacid amide at a ratio of about 7/3) differing in the weight ratio[(A-1)/fatty acid amide weight ratio] were used (both the componentswere present in the form of independent particles).

A-2:

(A-1)/fatty acid amide ratio=10/1

A-3:

(A-1)/fatty acid amide ratio=10/2.5

A-4:

(A-1)/fatty acid amide ratio=10/5

A-5:

(A-1)/fatty acid amide ratio=10/10

A-6:

(A-1)/fatty acid amide ratio=10/25

The following solid solutions of Crystal Violet Lactone (A-1) and thefatty acid amide according to the present invention (present in the formof compatible solid particles of both the components) were used.

Each solid solution was prepared by dissolving 10 parts by weight (allof "parts" given hereinafter are by weight) of Crystal Violet Lactoneand a predetermined amount of the above-mentioned fatty acid amide in 35to 60 parts of diacetone alcohol under heating at 120° C., mixing thesolution with 500 parts of water and filtering, water-washing and drying(60° C.) the formed precipitate.

A-7:

Solid solution of A-2

A-8

Solid solution of A-3

A-9:

Solid solution of A-4

A-10:

Solid solution of A-5

A-11:

Solid solution of A-6

In a ball mill, 10 parts of the leuco pigment A-1, the mixture A-2, A-3,A-4, A-5 or A-6 or the solid solution A-7, A-8, A-9, A-10 or A-11, 67parts of an aqueous solution containing 5% by weight of polyvinylalcohol and 10 parts of water were mixed and pulverized for 5 hours toobtain a liquid A' (A'-1 through A'-11).

Preparation of Color Developer Dispersion (Liquid B)

In a ball mill, 100 parts of 2,4-dihydroxybenzophenone, 670 parts of anaqueous solution containing 5% by weight of polyvinyl alcohol and 100parts of water were mixed and pulverized for 5 hours to form a liquid B.

Preparation of Heat-Sensitive Recording Paper and Color Formation Test

The liquid A' was mixed with the liquid B so that the amount of thephenolic color developer was 5 times the amount of Crystal VioletLactone on the weight base to form a coating liquid. The coating liquidwas coated on a slick paper having a basis weight of 55 g/m² by a wirebar and dried at 60° C. to obtain a heat-sensitive recording paperhaving a coating amount of about 5 g/m². The recording paper was passedat a speed of 4 cm/sec between rotary heater rollers (pressed under 1Kg/cm) at a heating temperature (roller surface temperature) shown inTable 7 to effect coloration under heating. The reflection density ofthe formed color was measured by a commercially available densitometer(Macbeth RD-514 with a red filter). The obtained results are shown inTable 7.

From the results shown in Table 7, it will readily be understood that incase of a mixed dispersion of the leuco pigment and the fatty acidamide, the density of the formed color is lower than the density of thecolor formed in case of the leuco pigment alone, whereas in case of asolid solution dispersion of the leuco pigment and the fatty acid amide,the density of the formed color is much higher than the density of thecolor formed when the leuco pigment alone is used. It will also be seenthat when the amount of the fatty acid amide exceeds 100% by weightbased on the leuco pigment in the solid solution, the density of theformed color is reduced at a higher temperature and that it is preferredthat the amount of the fatty acid amide be 5 to 100% by weight based onthe leuco pigment.

                  TABLE 7                                                         ______________________________________                                                    Reflection Density                                                Form of Leuco                                                                             Heating Temperature (°C.)                                  Pigment     90     100     110  120   130  140                                ______________________________________                                        A-1 alone   0.07   0.20    0.38 0.70  0.82 1.10                               dispersed mixture                                                             particles                                                                     A-2         0.07   0.13    0.22 0.48  0.68 0.96                               A-3         0.09   0.15    0.27 0.58  0.86 1.00                               A-4         0.08   0.14    0.26 0.45  0.62 0.76                               A-5         0.07   0.13    0.22 0.42  0.60 0.77                               A-6         0.07   0.11    0.18 0.38  0.56 0.73                               compatible solid                                                              particles (solid                                                              solution)                                                                     A-7         0.30   0.54    0.78 0.89  1.05 1.10                               A-8         0.36   0.68    0.90 0.99  1.07 1.13                               A-9         0.28   0.46    0.66 0.88  0.94 1.00                               A-10        0.22   0.56    0.77 0.87  0.93 0.90                               A-11        0.22   0.56    0.81 0.84  0.80 0.76                               ______________________________________                                    

EXAMPLE 9

In the same manner as described in Example 8, heat-sensitive recordingpapers were prepared from combinations shown in Table 8.

The obtained heat-sensitive recording papers were passed through heaterrollers in the same manner as described in Example 8 and the reflectiondensities of the formed colors were measured. The obtained results areshown in Table 9.

                                      TABLE 8                                     __________________________________________________________________________    Combina-      Compatible Organic         Phenolic Color                       tion Leuco Pigment                                                                          Solid Medium                                                                            Form and Weight Ratio of Particles                                                             Developer                                                                              Binder                      __________________________________________________________________________    (1)-a                                                                              fluoran type leuco                                                                     --        dispersed single substance                                                                     p-vinylphenol                                                                          polyvinyl                        pigment(green)     particles        polymer  alcohol                          color forming,                      (m.p. = 190° C.)                   m.p. = 163°)                                                      (1)-b                                                                              fluoran type leuco                                                                     fatty acid amide*.sup.1                                                                 dispersed mixture particles                                                                    p-vinylphenol                                                                          polyvinyl                        pigment (green                                                                         (m.p. = 108°C.)                                                                  (10/2.5)         polymer  alcohol                          color forming,                      (m.p. = 190° C.)                   m.p. = 163°)                                                      (1)-c                                                                              fluoran type leuco                                                                     fatty acid amide*.sup.1                                                                 dispersed solid solution particles                                                             p-vinylphenol                                                                          polyvinyl                        pigment (green                                                                         (m.p. = 108° C.)                                                                 (10/2.5)         polymer  alcohol                          color forming,                      (m.p. = 190° C.)                   mp. = 163°)                                                       (2)-a                                                                              fluoran type leuco                                                                     --        dispersed single substance                                                                     4,4'-thio-bis                                                                          etherified                       pigment (green     particles        (6-tert-butyl                                                                          starch*.sup.2                    color forming,                      3-methylphenol)                           m.p. = 163°)                 (m.p. = 160° C.)              (2)-b                                                                              fluoran type leuco                                                                     fatty acid amide*.sup.1                                                                 dispersed mixture particles                                                                    4,4'-thio-bis                                                                          etherfied                        pigment (green                                                                         (m.p. = 108° C.)                                                                 (10/2.5)         (6-tert-butyl-                                                                         starch*.sup.2                    color forming,                      3-methylphenol                            m.p. = 163°)                 (m.p. = 160° C.)              (2)-c                                                                              fluoran type leuco                                                                     fatty acid amide*.sup.1                                                                 dispersed solid solution                                                                       4,4'-thio-bis                                                                          etherified                       pigment (green                                                                         (m.p. = 108° C.)                                                                 particles (10/2.5)                                                                             (6-tert-butyl-                                                                         starch*.sup.2                    color forming,                      3-methylphenol)                           m.p. = 163°)                 (m.p. = 160° C.)              (3)-a                                                                              Crystal Violet                                                                         --        dispersed single substance                                                                     2,2-bis(4'-                                                                            etherified                       Lactone (m.p. =    particles        hydroxyphenyl)                                                                         starch*.sup.2                    180° C.)                     propane                                                                       (m.p. = 156° C.)              (3)-b                                                                              Crystal Violet                                                                         oxidized polyethy-                                                                      dispersed mixture particles                                                                    2,2-bis(4'-                                                                            etherified                       Lactone (m.p. =                                                                        lene (m.p. = 98° C.)                                                             (10/1)           hydroxyphenyl)                                                                         starch*.sup.2                    180° C.)                     propane                                                                       (m.p. = 156° C.)              (3)-c                                                                              Crystal Violet                                                                         oxidized polyethy-                                                                      dispersed solid solution particles                                                             2,2-bis(4'-                                                                            etherified                       Lactone (m.p. =                                                                        lene (m.p. = 98° C.)                                                             (10/1)           hydroxyphenyl)                                                                         starch*.sup.2                    180° C.)                     propane                                                                       (m.p. = 156° C.)              (4)-a                                                                              Crystal Violet                                                                         --        dispersed single substance particles                                                           2,2-bis(4'-                                                                            etherified                       Lactone (m.p. =                     hydroxyphenyl)                                                                         starch*.sup.2                    180° C.)                     propane                                                                       (m.p. = 156° C.)              (4)-b                                                                              Crystal Violet                                                                         4-vinylpyridine                                                                         dispersed moisture particles                                                                   2,2-bis(4'-                                                                            etherfied                        Lactone (m.p. =                                                                        polymer (s.p =                                                                          (10/2.5 )        hydroxphenyl)                                                                          starch*.sup.2                    180° C.)                                                                        110° C.)            propane                                                                       (m.p. = 156° C.)              (4)-c                                                                              Crystal Violet                                                                         4-vinylpyridine                                                                         dispersed solid solution particles                                                             2,2-bis(4'-                                                                            etherfied                        Lactone (m.p. =                                                                        polymer (s.p =                                                                          (10/2.5)         hydroxphenyl)                                                                          starch*.sup.2                    180° C.)                                                                        110° C.)            propane                                                                       (m.p. = 156° C.)              __________________________________________________________________________     Note:                                                                         *.sup.1 formaldehyde condensate of a mixture containing stearic acid amid     and palmitic acid amide at a ratio of about 7/3                               *.sup.2 used in the form as aqueous solution having a concentration of 20     by weight                                                                

                  TABLE 9                                                         ______________________________________                                        Combination                                                                            Heating Temperature (°C.)                                                                Reflection Density*                                ______________________________________                                        (1)-a    160               0.32                                               (1)-b    160               0.73                                               (1)-c    160               1.19                                               (2)-a    150               0.70                                               (2)-b    150               1.00                                               (2)-c    150               1.28                                               (3)-a    110               0.40                                               (3)-b    110               0.39                                               (3)-c    110               0.76                                               (3)-a    130               0.85                                               (3)-b    130               1.00                                               (3)-c    130               1.31                                               (4)-a    130               0.85                                               (4)-b    130               0.88                                               (4)-c    130               1.23                                               ______________________________________                                         Note:                                                                         *neutral filter was used for the measurement of the green color          

From the results shown in Table 9, it will readily be understood that ineach combination, a color having a higher density is obtained in arecording paper prepared by using the leuco pigment and organic solidmedium in the form of compatible solid particles.

A similar tendency was observed when a Rhodamine lactam type leucopigment, a spiropyran type leuco pigment, an Auramine type leuco pigmentor a phenothiazine type leuco pigment was used instead of theabove-mentioned leuco pigment.

EXAMPLE 10

A solid solution was prepared from an organic solid medium shown inTable 10 and Crystal violet Lactone, and in the same manner as describedin Example 8, a heat-sensitive recording paper was prepared by using theso prepared solid solution, 2,2-bis(4'-hydroxyphenyl)propane as a colordeveloper and a 5% by weight aqueous solution of polyvinyl alcohol as abinder. The recording paper was passed through heater rollers to examinethe color-forming property. The obtained results are shown in Table 10.

                  TABLE 10                                                        ______________________________________                                                      Pigment/   Heating Tem-                                                                             Reflec-                                                 Medium     perature   tion                                      Organic Solid Medium                                                                        Weight Ratio                                                                             (°C.)                                                                             Density                                   ______________________________________                                        --            10/0       140        1.05                                      low density polyethy-                                                                       10/2       140        1.28                                      lene(m.p. = 110° C.)                                                   zinc dibutyldithiocar-                                                                      10/1       140        1.22                                      bamate(m.p. = 103° C.)                                                 styrene homopolymer                                                                         10/2       140        1.27                                      (s.p = 125° C.)                                                        microcrystalline wax                                                                        10/1       140        1.29                                      (m.p. = 110° C.)                                                       zinc stearate (m.p. =                                                                       10/1       140        1.28                                      122° C.)                                                               ______________________________________                                    

In each case, the density of the formed color was higher than thedensity of the color formed when the leuco pigment was not formed into asolid solution.

The solid solutions described hereinbefore were prepared according tothe method described in Example 8, that is, the first method describedin the text of the instant specification. When low density polyethyleneor zinc stearate is used, the second method may be adopted, and whenmicrocrystalline wax is used, the third method may be adopted.

EXAMPLE 11

In 250 parts of diacetone alcohol were dissolved 100 parts of2,2'-bis(4'-hydroxyphenyl)propane and 10 parts of erucic acid amide(having a melting point of 79° C.) under heating, and the formedsolution was poured into 3600 parts of water to precipitate a solidsolution of the color developer. The precipitate was recovered byfiltration, washed with water and dried at 60° C. For comparison, acolor developer composed of a mixture containing2,2'-bis(4'-hydroxyphenyl)propane and erucic acid amide at a weightratio of 10/1 was separately prepared. The so-formed solid solution wascombined with the leuco pigment solid solution (3)-c of Example 9, and aheat-sensitive recording paper was prepared in the same manner asdescribed in Example 8. The recording paper was passed through heaterrollers (surface temperature=100° C.). The density of the formed colorwas 1.05. When the comparative color developer was used, the density ofthe formed color was only 0.80.

What I claim is:
 1. A heat-sensitive color-forming recording materialwhich comprises a recording layer comprising a particulate phenoliccolor developer and a particulate leuco pigment, which are dispersed ina binder independently from each other, wherein the phenolic colordeveloper and/or leuco pigment is present in the form of compatiblesolid particles with a substantially inactive organic solid mediumselected from the group consisting of sterically hindered phenolcompounds, said organic solid medium having a melting or softening pointlower than that of the phenolic color developer and/or leuco pigment andsaid organic solid medium is present in said compatible solid particlesin an amount .[.2 to 250 times as large as.]. .Iadd.of 0.2 to 250% byweight, based on .Iaddend.the amount of the phenolic color developerand/or leuco pigment on the weight base.
 2. A recording material as setforth in claim 1, wherein the organic solid medium is present in anamount of 5 to 100% by weight based on the phenolic color former and/orleuco pigment.
 3. A recording material as set forth in claim 1, whereinthe number average particle size of the compatible solid particles is0.1 to 3 microns.
 4. A recording material as set forth in claim 1,wherein the binder is a water-soluble or water-dispersible binder.
 5. Arecording material as set forth in claim 1, wherein the recording layercontains the leuco pigment and the phenolic color former at a weightratio of from 1/2 to 1/40 and the amount of the leuco pigment is 2 to30% by weight based on the total recording layer.
 6. A recordingmaterial as set forth in claim 1 wherein the organic solid medium is asterically hindered phenol selected from the group consisting of2,6-di-tert-butyl-p-cresol,2,2-methylene-bis(4-ethyl-6-tertbutylphenol),2-hydroxy-4-methoxybenzophenone, phenyl salicylate, p-tert-butylsalicylate and 2-(2'-hydroxy-5'-methylphenyl)-benzotriazole.